The present invention relates to a method of designing a photosensitive composition and a lithography process and particularly to a method of designing a photosensitive composition containing an acid generating agent and a lithography process using the photosensitive composition.
In the process of fabricating a semiconductor device, a photosensitive composition (so-called resist) is patterned by a lithographic treatment, and etching is conducted by using the pattern of the photosensitive composition as a mask.
Accordingly, as demand has increased for a finer semiconductor device in recent years, shortening of the wavelength of exposure radiation has been progressing in pattern exposure in the lithographic treatment. Therefore, in addition to lithography with the KrF excimer laser light presently used, lithography processes using ArF, F2, EUV, X-rays, charged particle beams such as electron beam or the like as exposure radiation have been proposed. On the other hand, in order to enhance the through-put in pattern exposure, a chemical amplification type photosensitive composition with a higher sensitivity has come to be used in lithography using such exposure radiations.
The chemical amplification type photosensitive composition contains an acid generating agent capable of generating an acid upon irradiation with the exposure radiation. Due to the presence of the acid generated in the photosensitive composition upon irradiation with exposure radiation, a cross-linking reaction proceeds in the photosensitive composition in the case of the negative type, while a decomposition reaction proceeds in the photosensitive composition in the case of the positive type. Accordingly, pattern exposure can be achieved with less exposure dose.
Meanwhile, in the case where enhancement of the sensitivity of the photosensitive composition proceeds, the irradiation amount of the exposure radiation (namely, exposure dose) onto an exposure area is decreased. FIG. 8 shows, by way of example, the relationship between the exposure dose in electron beam lithography and the average distance between exposure particles in the exposure area. As shown in the figure, the average distance between the exposure particles in the exposure area increases as the exposure dose is decreased by the enhancement of sensitivity, and it is seen that the statistic dispersion of the exposure particles in the exposure area at the time of pattern exposure is greater as the sensitivity of the photosensitive composition is higher. This becomes conspicuous when the sensitivity is enhanced from the sensitivity realized in electron beam lithography at present (exposure dose 5 xcexcC/cm2) to a higher sensitivity of not more than 1 xcexcC/cm2. In addition, where the efficiency of generation of acid in relation to the incident electrons (exposure particles) is low, the average distance between the acids is enlarged accordingly, and the statistic dispersion of the locations of presence of the acid contributing to the reaction of the photosensitive composition is enlarged.
It is known that, where the statistic dispersion of the exposure particles in the exposure area is thus enlarged, the edge roughness of end portions of a resist pattern formed by lithography is enlarged due to the statistic dispersion of the exposure particles, as described in Article 1 in the Journal of Vacuum Science and Technology, B17[6] (1999-11, 12) (USA) Wolfgang Henke and Michael Torkler, p.3112-3118. This applies also to the above-mentioned chemical amplification type photosensitive composition, and the enlargement of the edge roughness causes a lowering in the resolution of the photosensitive composition.
Accordingly, it is an object of the present invention to provide a method of designing a chemical amplification type photosensitive composition capable of forming a pattern with a sufficient resolution, irrespectively of the sensitivity of the photosensitive composition and even where the sensitivity is further enhanced, and a lithography process using the chemical amplification type photosensitive composition.
In order to attain the above object, the method of designing a photosensitive composition according to the present invention is a method of designing a chemical amplification type photosensitive composition containing an acid generating agent and is characterized by the following procedure. First, the average distance between exposure particles in an exposure area of the photosensitive composition at the time of pattern exposure of the photosensitive composition is calculated based on the sensitivity required of the photosensitive composition. Next, the composition of the photosensitive composition is so that the average value of diffusion length of the acid generated from the acid generating agent upon pattern exposure is greater than the calculated average distance between the exposure particles.
According to the designing method discussed above, the composition of the photosensitive composition is set so that the acid generated from the acid generating agent diffuses with a diffusion length greater than the average distance between the exposure particles. Therefore, in the photosensitive composition, when pattern exposure is conducted, the acid generated upon the pattern exposure diffuses over a wide range in excess of the average distance between the exposure particles. Accordingly, even where the photosensitive composition has a high sensitivity, so that the exposure dose at the time of pattern exposure is small and the statistic dispersion of the exposure particles in the photosensitive composition is large, the edge roughness arising from the dispersion is mitigated.
Another designing method according to the present invention is a method in which the average distance between the acids generated from the acid generating agent upon pattern exposure is calculated, and the composition of a photosensitive composition is set so that the average value of diffusion length of the acid in the photosensitive composition is greater than the calculated average distance. According to such a designing method, when the pattern exposure is carried out, the acid generated upon the pattern exposure diffuses over a wide range in excess of the average distance between the acids. Therefore, even where the photosensitive composition has a high sensitivity, so that the exposure dose at the time of pattern exposure is small and the statistic dispersion of the exposure particles in the photosensitive composition is large, namely, where the statistic dispersion of the acid is large, the edge roughness arising from the dispersion is mitigated. In addition, in this designing method, designing is so conducted that the diffusion length of the acid exceeds the average distance between the acids, and, accordingly, even where the efficiency of generation of the acid in relation to the exposure particles is low, the statistic dispersion of the acid contributing to the reaction of the photosensitive composition is mitigated, and mitigation of the edge roughness is securely contrived.
The lithography process according to the present invention is a lithography process in which a chemical amplification type photosensitive composition containing an acid generating agent is subjected to pattern exposure, and thereafter a developing treatment is carried out; and it is characterized by the following procedure. First, the average distance between exposure particles in an exposure area of the photosensitive composition at the time of pattern exposure is calculated based on the exposure dose at the time of the pattern exposure. Next, lithography conditions, for example, heating conditions of the photosensitive composition before and after the pattern exposure, and concretely, heating temperature, heating period, heating atmosphere and the like, are set so that the average value of the diffusion length of the acid generated from the acid generating agent upon pattern exposure is greater than the calculated average distance between the exposure particles.
According to such a lithography process, the heating temperature conditions for the photosensitive composition before and after the pattern exposure are set so that the acid generated from the acid generating agent in the photosensitive composition upon pattern exposure diffuses with a diffusion length greater than the average distance between the exposure particles. Therefore, in the photosensitive composition, the acid generated by the pattern exposure diffuses over a wide range in excess of the average distance between the exposure particles. Accordingly, even where the pattern exposure is carried out with a low exposure dose and the statistic dispersion of the exposure particles in the exposure area is large, the dispersion is alleviated by the diffusion of the acid.
Another lithography process according to the present invention is a process in which the average distance between the acids generated from the acid generating agent upon pattern exposure is calculated, and lithography conditions are set so that the average value of the diffusion length of the acid in the photosensitive composition is greater than the calculated average distance. According to such a lithography process, in the photosensitive composition, the acid generated by the pattern exposure diffuses over a wide range in excess of the average distance between the acids. Therefore, even where the pattern exposure is carried out with a low exposure dose and the statistic dispersion of the exposure particles in the exposure area is large, namely, where the statistic dispersion of the acid generation is large, the dispersion is alleviated by the diffusion of the acid. In addition, according to this lithography process, the conditions are set so that the diffusion length of the acid exceeds the average distance between the acids, so that even where the efficiency of the generation of the acid in relation to the exposure particles is low, mitigation of the statistic dispersion of the acid contributing to the reaction of the photosensitive composition can be contrived.